A conventional rotor for motors is equipped with P (P denotes a number and in this example, P is two) permanent magnets 101 which are disposed on a surface of a rotor core disposed on a rotary shaft in a circumferential direction of the rotary shaft and arranged to be adjacent to each other, as shown in FIG. 18. However, a motor which employs a rotor of this kind has the following problems: high-frequency current ripples are generated by carrier frequency of an inverter to induce higher harmonic iron loss in a stator core and a permanent magnet of the motor, and what is more, torque ripples are increased. At high speed rotation, so-called field-weakening control is carried out to suppress an increase in induction voltage by advancing a current phase angle. This leads to a rapid decrease in torque. Then, as shown in FIG. 19 (Patent Reference 1: Japanese Patent No. 3659012), a rotor for motors has been proposed, including two permanent magnets 101 and two salient poles 103 made of a magnetic material, which are alternately disposed in a circumferential direction of a rotary shaft. In this rotor for motors, the generation of torque ripples is suppressed due to the existence of the salient poles 103.
Japanese Patent Publication No. 08-23664 (Patent Reference 2) has disclosed a rotor for motors which comprises first and second divided rotor magnetic pole units. The first divided rotor magnetic pole unit includes a plurality of permanent magnet magnetic pole portions of a first kind and a plurality of salient pole portions of a first kind made of a magnetic material, which are arranged alternately on a surface of a rotor core in a circumferential direction of a rotary shaft. The second divided rotor magnetic pole unit includes a plurality of permanent magnet magnetic pole portions of a second kind and a plurality of salient pole portions of a second kind made of a magnetic material, which are arranged alternately on the surface of the rotor core in the circumferential direction of the rotary shaft. In this rotor for motors, the generation of torque ripples is suppressed by arranging a pole arc angle of the permanent magnet magnetic pole portion of the first kind and that of the permanent magnet magnetic pole portion of the second kind to be different, and by arranging an open angle of the salient pole portion of the first kind and that of the salient pole portion of the second kind to be different.
Japanese Patent Publication No. 01-122353 has shown in FIG. 6 a rotor for motors, which comprises a rotor core, and first and second divided rotor magnetic pole units. The first divided rotor magnetic pole unit includes p (P is a positive even number) permanent magnet magnetic pole portions of a first kind which are disposed on a surface of the rotor core. The second divided rotor magnetic pole unit includes P (P is the positive even number) permanent magnet magnetic pole portions of a second kind which are disposed on the surface of the rotor core. A pole arc angle of the permanent magnetic pole portion of the first kind is smaller than that of the permanent magnet magnetic pole portion of the second kind. As shown in FIGS. 1 and 16 of this publication, however, permanent magnets 12a, 12b are joined onto a yoke 9. An outer surface of the yoke 9 is merely exposed between adjacent permanent magnets in the circumferential direction.
Japanese Patent Publication No. 2002-272066 has shown in FIG. 6 a rotor for motors, in which a magnetic binder 20 is filled into between permanent magnets 35 disposed on a yoke 11. The magnetic binder has been obtained by kneading permanent magnetic powder with an adhesive agent. However, the rotor shown in this publication is not equipped with first and second divided rotor magnetic pole units. In this rotor, gaps formed between the adjacent permanent magnets 35 are large in size and are formed when the permanent magnets 35 are disposed on the polygonal yoke 11. These gaps are not due to size precision of the permanent magnet magnetic pole portions. In this publication, the binder 20 to be filled into between the permanent magnets 35 is obtained by kneading permanent magnetic powder with an adhesive agent, and is called as a magnetic binder. The permanent magnet powder used in the binder 20 is a ferromagnetic material having high retention. It is a magnetic material having high magnetic resistance. The binder 20 including the permanent magnet powder works to extend the adjacent permanent magnets and make a portion filled with the binder 20 equivalent to the permanent magnet, thereby reducing cogging torque.
A motor which uses such kind of rotor for motors includes a Hall element for detecting a magnetic pole position disposed on a stator, in order to switch current to an armature of the stator in accordance with a position of the rotor. The Hall element for detecting a magnetic pole position is usually disposed in the vicinity of an edge of the permanent magnet that is located in the axial direction of the rotary shaft. However, in the rotor having the salient pole portion like the one shown in FIG. 19 (refer to Patent Reference 1), disturbance of magnetic flux T1 occurs in the vicinity of the zero crosses of a flux density wave (wave indicative of a relationship between the rotation angle of the rotor and density magnetic flux leaking out from the gap in the axial direction) which is detected by the Hall element for detecting a magnetic pole position, as shown in FIG. 20. Accordingly, the flux density wave may hardly be formed in a waveform of sine wave, causing a detection error of the magnetic pole position. Although the existence of the salient pole portion may reduce the torque ripples, a motor torque will be reduced.
In the rotor that does not have the salient pole portion like the one shown in FIG. 18, although no significant reduction of the motor torque is observed, the torque ripples cannot be reduced. In this rotor, a gap is formed due to size precision of the permanent magnet between the permanent magnets. The gap may cause disturbance of magnetic flux T2 in the flux density wave, as shown in FIG. 21.
Also in the rotor for motors disclosed in Patent Reference 2, disturbance of magnetic flux may occur in the vicinity of the zero crosses of the flux density wave and the wave may hardly be formed in a sine wave, possibly causing malfunction.